CVE-2021-23409Network attack vector

Denial of service via header read timeout omission

Published Jul 21, 2021 · Updated Sep 16, 2024

Denial of service in Pires go-proxyproto before 0.6.0 allows remote attackers to exhaust server resources via TCP connections without PROXY headers. The Listener.Accept path waits indefinitely for a PROXY protocol header because no read deadline is imposed, leaving each connection occupied until it sends data or closes. Any network-facing application that embeds the library and accepts attacker-controlled connections can be starved of connection resources, interrupting service without providing data or code execution.

CVSS severity7.5
High
EPSS probability1.65%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Pires go-proxyproto before 0.6.0 allows remote attackers to exhaust server resources via TCP connections without PROXY headers. The Listener.Accept path waits indefinitely for a PROXY protocol header because no read deadline is imposed, leaving each connection occupied until it sends data or closes. Any network-facing application that embeds the library and accepts attacker-controlled connections can be starved of connection resources, interrupting service without providing data or code execution.

The record

CVE
CVE-2021-23409
Published
Jul 21, 2021
Updated
Sep 16, 2024
Vendor
Pires
Product
go-proxyproto
Classifications
CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <0.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Pires · go-proxyprotoversion=unspecified <0.6.0

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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